Optical waveguides embedded in materials such as silicon, lithium niobate, and potassium titanyl phosphate (KTP) have found many important applications such as wavelength division multiplexing and demultiplexing, phase modulation and laser stabilization. Other applications are related to phase control of channel waveguides, wavelength tuning with a Bragg waveguide, and low voltage poling of an electro-optic material. Many of these applications require an electric field to pass through the waveguide. The electric field may be generated by pairs of electrodes attached to one or more surfaces of the waveguide substrate. The electric field generated by the electrodes may be used for one of two purposes, either to change the index of refraction of the waveguide material or to change the dipole moment of the waveguide material.
A change in the index of refraction of the waveguide material may be used to control the characteristics of the radiation as it propagates through the waveguide. Some of these characteristics are its phase, center wavelength reflected by a Bragg grating, beam steering, and spatial mode profile. A change in the dipole moment of the waveguide material may be used to create quasi-phase-matched waveguides, which in turn may be used for second harmonic generation and various other forms of nonlinear frequency conversion.
There are two common approaches to apply this electric field through the waveguide, both approaches having the electrodes mounted on the same substrate which houses the waveguide. The first approach has the electrodes on opposite surfaces of the substrate with the waveguide sandwiched between the electrodes. The second approach has the electrodes on the same surface of the substrate, the electrodes straddling the waveguide. Both approaches typically require photo-lithographic procedures applied directly to the substrate material which houses the waveguide. Also, in this configuration it is typical to deposit the electrodes on the substrate after the waveguide region has been defined by diffusion, ion exchange, or other acceptable processing steps. In the event that problems arise during the electrode deposition steps, the entire substrate may be rendered useless. For example, the electrode mask pattern may be improperly aligned to the substrate geometry yielding unacceptable results. Also, in some cases there may be a high density of multiple components on the same substrate material. Given this the loss of an entire substrate may represent significant financial loss.